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The Big Muskie was a model 4250-W Bucyrus-Erie dragline (the only one ever built). With a 220-cubic-yard (170 m3) bucket, it was the largest single-bucket digging machine ever created and one of the world's largest mobile earth-moving machines. It cost $25 million in 1969, the equivalent of $161 million today adjusted for inflation. Big Muskie was powered by electricity supplied at 13,800 volts via a trailing cable, which had its own transporter/coiling units to move it. The electricity powered the main drives, eighteen 1,000 horsepower (750 kW) and ten 625 horsepower (466 kW) DC electric motors. Once it had stripped all the overburden in one area of the pit, it could move itself short distances (usually less than a mile) to another pre-prepared digging position using massive hydraulic walker feet, although due to its 13,500 ton weight it traveled very slowly (1.76 inches per second (4.5 cm/s), roughly 0.1 mph) and required a carefully graded travelway with a roadbed of heavy wooden beams to avoid sinking into the soil and tipping over or getting stuck. During its 22 years of service, Big Muskie removed more than 608,000,000 cubic yards (465,000,000 m3) of overburden, twice the amount of earth moved during the construction of the Panama Canal, uncovering over 20,000,000 tonnes (22,000,000 short tons) of Ohio brown coal.